1. Field of the Invention
This invention relates to layered structures used as source electrodes, drain electrodes, and other electrodes of thin-film transistors, reflecting electrodes, wiring for connection between these electrodes, storage capacitor electrodes, and common electrodes used in thin-type display devices, and the manufacturing method of such layered structures.
2. Description of the Related Art
Because of low specific resistance and easy workability, Al alloys are used as thin-film materials for wiring film, electrode film, reflecting electrode film, storage capacitor electrode film, and common electrode film in the fields of liquid display devices, plasma display devices, electroluminescence display devices, field-emission display devices, and other flat panel display devices (FPD).
For example, Japanese Patent Application Laid-open Publication No. 11-352515 describes a layered structure in which a layer of Al alloy, a low-resistance metal, is formed over ITO layer or transparent oxide conducting layer.
As to the electrical characteristic of such layered structures, the electrical resistivity of the Al alloy and the contact resistance between the transparent oxide conducting layer and the Al alloy are required to be low.
When a layered structure was used, for example, for the scanning line or the signal line of a liquid crystal display device, the conventional layered structure had no problem concerning the contact resistance between the Al alloy and the transparent oxide conducting layer, since the wiring width was long and wide and the area in contact with the transparent oxide conducting layer was broad. However, as the liquid crystal panels have become high-resolution, wirings have become narrow-pitched, picture cells have become of high aperture ratio, and wirings have become thinner, the contact resistance between the Al alloy and the transparent oxide conducting layer has grown to be no longer a matter negligible.
Also, in patterning the layered structure formed on the substrate and made of the Al alloy and the transparent oxide conducting layer, the use of developing solution for photoresist (for example, a solution consisting primarily of TMAH [=tetramethyl ammonium hydride]) involved galvanic corrosion taking place in the Al alloy causing Al alloy to come off from the ITO film. It is conceived that such galvanic corrosion was caused because there was a large difference in the electrode potentials between the aluminum in electrolyte fluid (for example, the above developing solution) and the transparent oxide conducting layer.
On the other hand, addition of alloy content to the aluminum is one way to reduce electrical contact resistance, but in that case, there is a problem in that the electrical resistance of the Al alloy layer itself is compelled to increase. Particularly when it is used for scanning lines and signal lines, the problem is that delay is caused in signal transfer speed. Therefore, there is a limit in the method of adding alloy content to the aluminum.